<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <li class="test"></li>
    <li class="test"></li>
    <li class="test"></li>
    <li class="test"></li>
    <li class="test"></li>
    <script>
        class P{
            constructor() {
                this.name = 'hello'
            }
        }
        let p = new P()

        let obj = {
            a: 1
        }
        Object.defineProperty(obj, 'b', {
            value: 2,
            // enumerable: true
        })
        Object.defineProperty(obj, 'c', {
            set(val) {
                this._c = val
                document.getElementById('app').innerHTML = 123
            },
            get() {
                return this._c
            }
        })

        for(let key in obj) {
            console.log(key)
        }
    </script>
</body>
</html>